1. Field of the Invention
The present invention relates to a process for producing ultrafine particles, and more particularly, it relates to a process for producing ultrafine particles of ceramics or metal without using the melting and pulverizing processes.
2. Description of the Prior Art
A remarkable progress has recently been made in the micromachining technology typified by the LSI (large scale integration) technology in electronics. The microforming and machining technology is necessary to produce extremely small components which are essential for the miniaturization of electronics machines and equipment with high performance and high reliability. Thus the development of this technology is urgently required. Such developmental works will be supported by the technology of producing ultrafine particles of ceramics or metal. For example, ultrafine particles permit the reduction of the thickness of the paste layer used as the thick film resistor which is one element on the circuit board of hybrid IC. The paste for this application is produced from a powder of ruthenium oxide or metallic ruthenium.
According to the conventional technology, ruthenium oxide is produced by heating ruthenium or ruthenium sulfide in an oxygen stream or oxidizing atmosphere, and metallic ruthenium is obtained by electrorefining. Ruthenium oxide produced by the dry method has to undergo a process for size reduction (below 1 .mu.m) which consumes a great deal of time and energy. In addition, with the conventional pulverizing process it is difficult to produce ruthenium oxide powder of narrow particle size distribution and high purity. This is true of metallic ruthenium powders. In other words, there has been no process for producing a high-performance material for micromachining.
In the case of ceramics as an electronics material, it is necessary to sinter ultrafine particles of ruthenium oxide, ferrite, barium titanate, or the like so that the raw material powder does not lose its characteristic properties. This is accomplished by using a very active assistant which is as fine as the ceramics. To be more specific, a low-melting glass powder of ultrafine particles of about 100 A in size is favourably used as this kind of assistant. This glass powder is conventionally produced by mixing, melting and crushing a low-melting glass. Therefore, the conventional process requires a great deal of time and energy for melting oxides at high temperature and crushing glass. Moreover, the glass powder thus obtained is not good in particle properties.